Combined burner-lance for fume suppression in molten metals

ABSTRACT

A burner-lance apparatus for burning large volumes of fluid fuels and especially adapted to fume suppression during refining of molten metals wherein a double flared passageway with a straight wall section therebetween is disposed in the nozzle for intermixing oxygen and natural gas. A tubular member for conveying oxygen terminates upstream of the passageway and natural gas is directed around the tubular member with the natural gas stream converging into the oxygen in the converging portion of the passageway. The intermixed gases pass through the straight wall section and then expand in the second flared or divergent passageway.

United States Patent Masella et al.

1541 COMBINED BURNER-LANCE FOR FUME SUPPRESSION IN MOLTEN METALS [72] Inventors: Anthony J. Masella, Chicago; Edward A.

Grobel, Mundelein, both of Ill.

[73] Assignee: Chemetron Corporation, Chicago, Ill. [22] Filed: Mar. 26, 1969 211 App]. No.: 810,727

[ 1 Feb. 1, 1972 3,202,201 8/l965 Masella et al ..239/l32.5 3,236,281 2/1966 Bain et al ..239/l32.3

FOREIGN PATENTS OR APPLICATIONS 513,556 2/1955 Italy ..266/34 674,705 l/l930 France ..239/l32.3

Primary ExaminerGerald A. Dost AttarneyNicholas M. Esser [57] ABSTRACT A burner-lance apparatus for burning large volumes of fluid fuels and especially adapted to fume suppression during refining of molten metals wherein a double flared passageway with a straight wall section therebetween is disposed in the nozzle for intermixing oxygen and natural gas. A tubular member for conveying oxygen terminates upstream of the passageway and natural gas is directed around the tubular member with the natural gas stream converging into the oxygen in the converging portion of the passageway. The intermixed gases pass through the straight wall section and then expand in the second flared or divergent passageway.

1 Claims, 4 Drawing Figures PATENTfiD FEB 1:972

Inverztor's ANTHONY .T. MASELLA EDWARD A. GaoaEa.

' at high velocities for melting and refining metals without causing large volumes of fumes to escape from a furnace thus contributing to the control of air pollution.

Burner devices for use in metal-treating furnaces and em:

'ploying converging-diverging passageways to effect an intermixing of the fuel and an oxidizing gas are quite common. For example in US. Pat. Nos. 3,236,281; 3,078,084; 3,202,201 and 3,232,748 such devices are exemplified. U.S. Pat. Nos. 3,078,084 and 3,236,281 disclose the intermingling of a fuel and oxygen in the diverging portion of a converging-diverging nozzle element. In the instance of US. Pat. Nos. 3,236,281 and 3,202,201 a fluid fuel and a gas are mixed by intersecting a gas stream with the fluid fuel prior to their flow into the converging portion of a converging-diverging nozzle. In employing burners of the type concerned with in this invention it is necessary that they be inserted from different positions in a metallurgical furnace. Attempts to design a burner so as to have the flame come into close direct contact with the surface of molten metal is shown in US. Pat. No. Re. 26,364.

None of the previously mentioned burners are specifically adapted for use in close contact with the surface of a molten metal bath during refining. Of prime importance is to have such a burner in which the flame does not pulsate and emerges in a smooth pattern from the burner. Nowhere in the prior art is this type of burner described which is essential if proper mixtures of oxygen and gas are to be employed so as to reduce oxidation of iron, which is thought to cause excessive fumes, and iron oxide particle emission.

It is an object of the presentinvention to provide a bumerlance apparatus and method of operating same in the refining of molten metals. It is another object of the present invention to provide a method and apparatus for combusting gaseous fuels in a manner which reduces fume formation during refining of molten metals and particularly in the refining of stainless steel to provide an economical recovery of chrome. It is yet another object of the invention to provide a novel bumerlance apparatus which can be easily manipulated to bring a flame into direct contact with the surface of the metal bath while refining the metal. It is still an object of the present invention to provide apparatus and method of burning fluid fuels with a straight and substantially nonpulsating flame. It is another object of the invention to provide an apparatus and method of refining molten metals to improve metal yield without impairing metallurgical quality.

SUMMARY OF THE INVENTION The foregoing objects are accomplished and the shortcomings of the prior art are overcome by the method and apparatus of the present invention wherein the novel combined bumer-lance effects the introduction of oxygen and a fluid fuel stream by an intersecting of the oxygen and the fluid fuel streams within the confines of a reducing diameter portion of a nozzle, subsequently flowing said intermixed stream through a straight wall portion and then expanding the intennixed streams by flowing them into an expanding diameter nozzle portion, which affords flame stabilization and provides excess oxygen for refining. A

BRIEF DESCRIPTION OF DRAWING A better understanding of the process and bumer-lance of this invention will be accomplished by reference to the drawing describing a preferred apparatus for effecting such method wherein:

FIG. 1 is a view in side elevation of the novel bumer-lance device.

FIG. 2 is an enlarged view in vertical section of the burnerlance device of FIG. 1.

FIG. 3 is an end view taken along line 3-3 of FIG. 2. FIG. 4 is a view in vertical section taken along line 4--4 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Briefly stated, the combined bumer-lance apparatus shown in the drawing directs a stream of substantially pure oxygen and a fluid fuel linearly and in separate and parallel streams with one of the streams directed outwardly and circumferentially of the other. A fluid fuel such as natural gas is directed in a manner to intersect with the inner oxygen gas stream and to be intermixed therewith. The inner oxygen stream is introduced into the outer natural gas stream at a point where the outer stream is directed toward the inner stream but in a manner not to substantially reduce the flow of natural gas. This effects a commingling of the natural gas and the oxygen in a first zone. After the commingling, the combined streams are passed through an intermediate zone wherein a uniform cross-sectional dimension of the stream is maintained. After the intermediate zone, the stream is directed into an expansion zone with some restriction where the fuel is combusted with some oxygen and the remaining oxygen used in combination with the fuel for refining. In a preferred manner, the inner oxygen stream is directed at a faster velocity thanthe outer natural gas stream to afford an aspirating effect.

The use of this particular method and apparatus is found to have particular advantages in the suppression of fumes in the refining of steel in metal-making furnaces. The flame should strike the surface of the molten metal at an angle in the range of about 3075 with the tip of the burner positioned as close to the surface of the slag as possible. Best results are effected with a molten steel bath at a temperature of about 3000" F. and with oxygen to natural gas ratios of from 2.521 up to 4:1 with best results being obtained when employing a 3:1 ratio.

The drawing illustrates the bumer-lance which has been found best to carry out the foregoing process. Bumer-lance 10 is formed from three concentrically positioned pipes 11, 12 and 13 composed of black iron pipe. Outer pipe 13 has two rounded end portions 15 and 16 and is welded to pipe 12 at the point designated by the numeral 17. Central pipe 11 forms a chamber 20 supplying oxygen through burner 10. Pipe 11 has two extensions 11a and 11b in order to effect the desired 45 angle between the main longitudinal axis of the burner and the minor nozzle portion 23. Similar extensions of pipes 12 and 13 are similarly designated. Disposed in nozzle portion 23 and in pipe 12 is double flared passageway 24 formed from two reducing diameter sections 25 and 26 with the smaller sections oppositely disposed and the passageway terminating coextensively with the end of the burner. A straight wall section 27 is positioned between sections 25 and 26 and has a length less than either of the conical sections. Oxygen pipe 11b extends a short distance into reduced diameter section 25 terminating at a point remote from straight wall section 27 and it is disposed concentrically therewith. It will be seen that the oxidizing gas tubular member. 11b has an outer diameter equal to the inner diameter of the straight wall section 27 with an inner diameter slightly smaller than the straight wall section. The double flared passageway 24 is formed from two frustoconical portions derived from slightly different cones and having slightly different wall lengths. The angle of taper of conical section 25 is slightly greater than that of section 26 with the wall length of section 25 being slightly longer than that of section 26.

Nozzle portion 23 is cooled by means of four pipes 30 which carry cooling water from chamber 31 to the tip of bumerlance 10 where the cooling water exits at the ends 33 of pipes 30. The heated water is returned along the outside of pipes 30, and in chamber 28 formed by pipe 13, to water outlet pipe 34. The closed chamber 28 as well as the proper positioning of pipes 30 is provided by sealing and spacing elements 35. Cool water enters chamber 31 by means of inlet pipe 37.

A fluidtight engagement and spacing of oxygen pipe 11 is provided by sealing element 40 which is welded to the inside of pipe 12 and the outside of pipe 11. This forms a closed tubular chamber 42 for natural gas which is introduced by means of inlet pipe 44.

The relative sizes of the pipes composing burner and the relative dimensions of the flared passageway 24 are important factors in providing efficient combustion with excess oxygen. Oxygen pipe 11 as well as extension elbow 11a and the nozzle portion llb are l-inch standard black iron schedule 40. Pipes 12, 12a and 12b are 2-inch standard black iron schedule 40 and pipes 13, 13a and 13b are 4-inch black iron standard schedule 40. Oxygen pipe 11b is disposed with its end 2% inches from the end of burner 10 and consequently, the end of flared passageway 24 which is positioned flush with the end of nozzle portion of burner 10. The distance from the end of passageway 24 at the nozzle portion of the burner to its opposing end adjacent oxygen pipe llb is 3% inches. The straight wall section 37 extends a distance of 1% inches and has an internal diameter of 1.315 inches. The length of the wall section comprising conical portion 26 is 1% inches while that composing conical section 25 is 1% inches.

OPERATION A better understanding of the foregoing described burnerlance can be had through an explanation of its operation with the flow of fluid materials therethrough when employing the bumer-lance in direct are electric steelmaking furnace during the refining stage. Oxygen pipe 11 is connected in a normal manner with a suitable supply of oxygen and also has a means for regulating and measuring the flow of oxygen to chamber 20. In a similar manner, gas inlet pipe 44 is connected to a suitable source of natural gas and also a regulatory and metering means. As the foregoing mentioned regulatory and metering mechanism is of a standard variety, they are not shown in the drawing. With cooling water flowing into pipes 30 from water inlet pipe 37, oxygen and natural gas are introduced from their respective sources into chambers and 42, respectively. The oxygen flows through pipes 11, lla and llb inwardly and linearly at a rate of about 21,000 cubic feet per hour from the natural gas stream flowing at a rate of about 7,000 cubic feet per hour between pipes 12, 12a and 12b and pipes 11, 11a and llb which places the natural gas stream outwardly and circumferentially of the inward oxygen stream. These volumes afford a stoichiometric excess of oxygen. As the natural gas approaches conical section it is directed inwardly toward the inner oxygen stream in a first compression zone where the oxygen and natural gas are commingled. Subscquently, the commingled stream is passed through straight wall section 27 wherein a uniform cross-sectional dimension for the commingled stream is maintained. Subsequently, the commingled stream enters conical section 26 which permits an expansion of the commingled stream with subsequent combustion of the fluid fuel in a smooth and nonturbulent manner. Best results are obtained when the natural gas stream is directed into the first zone composed of conical section 25 at a slower velocity than the inner oxygen stream. The cooling water which emerges through the end of pipe 30 at point 33 is returned along the outer side of pipe 12 between pipes 12 and 13 and their respective extensions to water outlet 34.

The previously described use of the three zones provides efficient combustion in a manner that the flame projecting from the tip of the burner is smooth and substantially quiet. The efficient combustion and smooth firing of the burner takes place even though the tip of the burner may be employed at very close distances from the slag and surface of a molten metal bath during refining to provide fume suppression and increase metallic yield.

It should be pointed out that the nozzle portion 23 of burner-lance 10 is constructed at 45 angle to the main axis of the burner-lance. This permits the direction of the flame at about a 30-75 angle when thc burner-lance is introduced into a furnace from a sidewall. This angle for the bumer-lance nozzle when combined with the double flared passageway has important advantages for the bumer-lance in the fumeless refining of metals. It should be indicated that while bumerlance 10 is described with a nozzle design at a 45 angle, the nozzle could be disposed along the same axis as the major portion of the burner-lance. Further, straight wall section 27 comprising the intermediate zone could be eliminated although best results are obtained when it is employed.

Burner-lance 10 is described for use in the refining of steel in an electric furnace. However, it can also be advantageously employed for scrap preheating in all of the well-known metaltreating furnaces.

Natural gas is described as the preferred fluid fuel. However, other fluid fuels of the gaseous type such as hydrogen or propane can be employed and liquid fuels such as fuel oil, pitch or tar. Pipes 11, 11a, llb, 12, 12a, 12b, 13, 13a and 13b are described as being composed of black iron. If desired, they could be fabricated from copper or stainless steel.

From the foregoing description of the present burner and process it is apparent that there is provided an apparatus and method for the combustion of fluid fuels which permits fumeless refining with efficient combustion. The present burner can be fabricated without the need of special tools or materials and also has a minimum number of parts. It can be easily manipulated and the flame brought into contact with the surface of a metal bath at an angle in the range of 30-75 even though the burner-lance is introduced from a sidewall.

It will be apparent that certain modifications and changes will be necessary for adaptation to specific materials from time to time as will be suggested to those skilled in the art. lt is intended that all such modifications and changes as come within the spirit of this invention are intended as being within its scope as best defined by the appended claims wherein there is claimed.

We claim:

1. An apparatus for fume suppression while refining molten metal by burning large volumes of combustible fluid fuel with an oxidizing gas comprising a first tubular member forming a first passage, a nozzle portion in fluid communication with said first tubular member, a double flared passageway in said nozzle portion including oppositely disposed conical sections derived from slightly different cones and having slightly different wall lengths and further including a substantially straight walled section between the smallest diameter portions of the respective conical sections, said substantially straight walled section having a length less than the length of either of said conical sections, a second tubular member forming a second passage, said second tubular member being concentrically positioned with respect to said double flared passageway and terminating within one of said conical sections at a point remote from the smallest diameter portion of said one of said conical sections, the outer wall of said second tubular member having an outer diameter substantially equal to the inner diameter of said substantially straight walled section and an inner diameter slightly smaller than the inner diameter of said substantially straight walled section, the other of said conical sections being constructed and arranged to provide expansion with some restriction of said fuel and oxidizing gas, inlet means communicating independently with said first and second tubular members, said conical section proximate to said tubular member having a taper slightly larger than the other conical section, and cooling means in heat exchange relationship with said nozzle portion to cool said nozzle portion. 

1. An apparatus for fume suppression while refining molten metal by burning large volumes of combustible fluid fuel with an oxidizing gas comprising a first tubular member forming a first passage, a nozzle portion in fluid communication with said first tubular member, a double flared passageway in said nozzle portion including oppositely disposed conical sections derived from slightly different cones and having slightly different wall lengths and further including a substantially straight walled section between the smallest diameter portions of the respective conical sections, said substantially straight walled section having a length less than the length of either of said conical sections, a second tubular member forming a second passage, said second tubular member being concentrically positioned with respect to said double flared passageway and terminating within one of said conical sections at a point remote from the smallest diameter portion of said one of said conical sections, the outer wall of said second tubular member having an outer diameter substantially equal to the inner diameter of said substantially straight walled section and an inner diameter slightly smaller than the inner diameter of said substantially straight walled section, the other of said conical sections being constructed and arranged to provide expansion with some restriction of said fuel and oxidizing gas, inlet means communicating independently with said first and second tubular members, said conical section proximate to said tubular member having a taper slightly larger than the other conical section, and cooling means in heat exchange relationship with said nozzle portion to cool said nozzle portion. 